The present invention relates to a two-cycle internal combustion engine which is suited for use in a portable power working machine, and in particular to a two-cycle internal combustion engine which is designed to introduce air into a combustion actuating chamber (though it may be also called combustion chamber, actuating chamber, cylinder chamber, etc., these chambers are generically referred to as combustion actuating chamber in the present specification) prior to the introduction of air-fuel mixture, thereby making it possible to minimize the quantity of so-called blow-by or the quantity of air-fuel mixture to be discharged without being utilized for the combustion.
An ordinary two-cycle gasoline engine which is conventionally used in a portable power working machine such as a chain saw and brush cutter is constructed such that an ignition plug is disposed at a head portion of a cylinder, and an intake port, a scavenging port and an exhaust port, which are to be opened and closed by a piston, are provided at the trunk portion of the cylinder. According to this two-cycle internal combustion engine, one cycle of engine is accomplished by two strokes of the piston without undergoing a stroke which is exclusively assigned to the intake or exhaust.
More specifically, in the ascending stroke of the piston, air-fuel mixture is introduced from the intake port into the crankcase disposed below the piston. When the piston is turned into a descending stroke, the air-fuel mixture is pre-compressed producing a compressed gas mixture, which is then blown into a combustion actuating chamber which is disposed above the piston, thereby enabling waste combustion gas to be discharged from the exhaust port. In other words, since the scavenging of the waste combustion gas is effected by making use of the gas flow of the air-fuel mixture, the unburnt air-fuel mixture is more likely to be mixed into the combustion waste gas (exhaust gas), thereby increasing the quantity of so-called blow-by or the quantity of air-fuel mixture to be discharged into air atmosphere without being utilized for the combustion. Because of this, the two-cycle internal combustion engine is not only inferior in fuel consumption but also disadvantageous in that a large amount of poisonous components such as HC (unburnt components in a fuel) and CO (incomplete combustion components in a fuel) are caused to be included into the exhaust gas as compared with a four-stroke engine. Therefore, even if the two-cycle engine is small in capacity, the influence of these poisonous components on the environmental contamination would not be disregarded.
With a view to cope with these problems, there have proposed various kinds of so-called air-preintroduction (lamellar scavenging) type two-cycle internal combustion engine, which are featured in that an air inlet passageway for introducing external air is attached to a scavenging passageway, thereby permitting air to be introduced into the combustion actuating chamber in the descending stroke of piston prior to the introduction of air-fuel mixture, the air thus pre-introduced functioning to form air layer between waste combustion gas to be discharged and unburnt air-fuel mixture to thereby prevent the unburnt air-fuel mixture from being mixed with the waste combustion gas, thus minimizing the quantity of blow-by of air-fuel mixture (for example, Japanese Patent Unexamined Publications H9-125966 and H5-33657, and Japanese Patent No. 3040758).
The present inventors have also already proposed an air-preintroduction type two-cycle internal combustion engine having a basic structure as explained below. (Japanese Patent Application 2000-318841).
Namely, this previously proposed two-stroke internal combustion engine which is featured in that one or more pairs of Schnxc3xcrle type scavenging passageways, each allowing the combustion actuating chamber disposed above the piston inside the cylinder to be communicated with the crank chamber, are symmetrically provided on both sides of the longitudinal section which imaginatively divides an exhaust port into two equal parts, thereby enabling air to be introduced into the scavenging passageways and also enabling an air-fuel mixture to be introduced into the crank chamber; and that in the descending stroke of the piston, the exhaust port is opened at first, and then, the scavenging port which is disposed at a downstream end of the scavenging passageway is opened, thereby enabling air to be introduced via the scavenging passageway into the combustion actuating chamber prior to the introduction of air-fuel mixture.
According to this two-stroke internal combustion engine proposed previously by the present inventors, an external air is sucked up and stored in the scavenging passageways and in the crank chamber through an air inlet passageway and an air check valve disposed in the air inlet passageway in the ascending stroke of piston, and at the same time, the air-fuel mixture supplied from an air-fuel mixture-generating means such as a carburetor is sucked up and stored in the crank chamber through an air-fuel mixture supply passageway and an air-fuel mixture inlet port.
When the air-fuel mixture inside the combustion actuating chamber disposed above the piston is exploded and burnt through the ignition thereof, the piston is pushed downward due to the combustion gas. In this descending stroke of the piston, the air as well as the air-fuel mixture existing inside the scavenging passageways and the crank chamber are compressed by the piston, and at the same time, the exhaust port is opened at first, and as the piston is further descended, the scavenging port provided at a downstream end of each of the scavenging passageways is opened. During this scavenging period where the scavenging port is kept opened, only the air that has been compressed by the piston and stored inside the scavenging passageways is permitted to be introduced from the scavenging port into the combustion actuating chamber.
Subsequently, when the piston is further descended, the introduction of air from the scavenging port into the combustion actuating chamber is accomplished, and then, the air-fuel mixture that has been pre-compressed in the crank chamber is permitted to be introduced, via the scavenging passageways, into the combustion actuating chamber until the scavenging period is finished.
Therefore, since air is introduced from the scavenging port into the combustion actuating chamber prior to the introduction of air-fuel mixture into the combustion actuating chamber in the descending stroke of the piston, the waste combustion gas is forced, due to this air, to go out of the exhaust port and scavenged therethrough, so that almost all of the combustion is not permitted to remain inside the combustion actuating chamber or any other portions including the region located close to the inner wall portion of cylinder which is located opposite to the exhaust port. Thereafter, the waste combustion gas is discharged through a muffler into the external atmosphere.
In this case, since a layer of the air that has been introduced in advance into the combustion actuating chamber through the scavenging port is permitted to be formed between the waste combustion gas and the air-fuel mixture that has been introduced belatedly into the combustion actuating chamber through the scavenging port, the air-fuel mixture can be effectively prevented from being mixed with the waste combustion gas due to this air layer. As a result, it is possible to realize a lamellar scavenging and to minimize the quantity of so-called blow-by, i.e. the quantity of air-fuel mixture to be discharged without being utilized for the combustion, thus making it possible to realize a reliable and perfect ignition of air-fuel mixture, to improve the fuel consumption, and to minimize the content of poisonous components in the exhaust gas.
However, according to this air-preintroduction (lamellar scavenging) type two-cycle internal combustion engine which has been previously proposed by the present inventors, since the effective cross-sectional passage area at the end portion of the scavenging passageway (upstream end=scavenging inlet port) which is located close to the crank chamber is generally almost equal to or larger than the downstream portion of the scavenging passageway, the air-fuel mixture introduced into the combustion actuating chamber is enabled to easily mix with the air that has been introduced in advance into the combustion actuating chamber during the scavenging period (especially, during the intermediate period through the last period thereof), thereby giving rise to the generation of incomplete lamellar scavenging.
The present invention has been made to overcome the aforementioned problems, and therefore an object of the present invention is to provide an air-preintroduction type two-cycle internal combustion engine which is capable of minimizing the possibility of air-fuel mixture being mixed with the air that has been introduced in advance into the combustion actuating chamber during the scavenging period, thereby enabling a complete lamellar scavenging to be performed.
With a view to realize the aforementioned objects, the two-cycle internal combustion engine according to the present invention is basically constructed such that one or more pairs of Schnxc3xcrle type scavenging passageways, each allowing the combustion actuating chamber disposed above a piston placed in a cylinder to be communicated with a crank chamber, are symmetrically provided on both sides of the longitudinal section which imaginatively divides an exhaust port into two equal parts, thereby enabling air to be introduced into the scavenging passageways and also enabling air-fuel mixture to be introduced into the crank chamber; and that in the descending stroke of the piston, the exhaust port is opened at first, and then, the scavenging port which is disposed at a downstream end of the scavenging passageway is opened, thereby enabling air to be introduced via the scavenging passageway into the combustion actuating chamber prior to the introduction of air-fuel mixture into the combustion actuating chamber.
This two-cycle internal combustion engine is characterized in that said one or more pairs of Schnxc3xcrle type scavenging passageways are respectively provided, near the end portion thereof located close to the crank chamber, with a throttled portion.
In a preferred embodiment, the paired scavenging passageways are combined with each other at the portion thereof located close to the crank chamber to thereby enlarge the volume thereof, and are communicated with the crank chamber via a common throttled portion for reducing the effective cross-sectional passage area to such an extent that it becomes smaller than that of the downstream portion of the scavenging passageway.
In another preferred embodiment, the scavenging passageways are provided respectively with an air inlet passageway for introducing air therein, and the air inlet passageway is provided with an air check valve.
In this case, the volume of the scavenging passageways is preferably set to such that it is equal to or slightly smaller than the quantity of air to be introduced in advance.
The effective cross-sectional passage area of the throttled portion is preferably set to such that a required quantity of air-fuel mixture can be fed to the combustion actuating chamber following the introduction of air thereto.
According to the preferable embodiments of two-cycle internal combustion engine of the present invention, which are constructed as described above, when the crank chamber is turned into a negative pressure in the ascending stroke of the piston, the external air is permitted to be sucked and stored in the air inlet passageway and in the scavenging passageways (the air may be introduced more or less into the crank chamber through the throttled portion), and at the same time, air-fuel mixture to be fed from the air-fuel mixture-generating means such as a carburetor is sucked up and stored in the crank chamber through an air-fuel mixture supply passageway and an air-fuel mixture inlet port.
When the air-fuel mixture inside the combustion actuating chamber disposed above the piston is exploded and burnt through the ignition thereof, the piston is pushed downward due to the combustion gas. In this descending stroke of the piston, the air as well as the air-fuel mixture existing inside the air inlet passageway, the scavenging passageways and the crank chamber are compressed by the piston, and at the same time, the exhaust port is opened at first, and as the piston is further descended, the scavenging port provided at a downstream end of each of the scavenging passageways is opened. During this scavenging period where the scavenging port is kept opened, only the air that has been compressed by the piston and stored inside the scavenging passageways is permitted to be introduced from the scavenging port into the combustion actuating chamber.
Subsequently, when the piston is further descended, the introduction of air from the scavenging port into the combustion actuating chamber is accomplished, and then, the air-fuel mixture that has been pre-compressed in the crank chamber is permitted to be introduced, via the scavenging passageways provided with the throttled portion, into the combustion actuating chamber until the scavenging period is finished.
Therefore, since air is introduced from the scavenging port into the combustion actuating chamber prior to the introduction of air-fuel mixture into the combustion actuating chamber in the descending stroke of the piston, the combustion exhaust gas is forced, due to this air, to go out of the exhaust port and scavenged therethrough, so that almost all of the combustion is not permitted to remain inside the combustion actuating chamber or any other portions including the region located close to the inner wall portion of cylinder which is located opposite to the exhaust port. Thereafter, the combustion exhaust gas is discharged through a muffler into the external atmosphere.
In this case, since a layer of the air that has been introduced in advance into the combustion actuating chamber through the scavenging port is permitted to be formed between the combustion exhaust gas and the air-fuel mixture that has been introduced belatedly into the combustion actuating chamber through the scavenging port, the air-fuel mixture can be effectively prevented from being mixed with the combustion exhaust gas due to this air layer. As a result, it is possible to realize a lamellar scavenging and to minimize the quantity of so-called blow-by, i.e. the quantity of air-fuel mixture to be discharged without being utilized for the combustion, thus making it possible to realize a reliable and perfect ignition of air-fuel mixture, to improve the fuel consumption, and to minimize the content of poisonous components in the exhaust gas.
Furthermore, according to the two-cycle internal combustion engine of the present invention, since a throttled portion is provided at the end portion of the scavenging passageway (upstream end=scavenging inlet port) which is located close to the crank chamber, air-fuel mixture can be hardly mixed with the air that has been sucked in advance into the scavenging passageway. As a result, the pre-introduction of air can be reliably performed, thereby making it possible to realize a more perfect lamellar scavenging.
Additionally, due to the provision of the throttled portion, air-fuel mixture can be introduced into the scavenging passageways from the crank chamber only when the pressure inside the crank chamber is increased to a certain magnitude. In other words, since the timing of introducing air-fuel mixture into the scavenging passageways from the crank chamber is slightly delayed as compared with the case where the aforementioned throttled portion is not provided, it becomes possible to realize a more perfect lamellar scavenging.
As a result, it is now possible to perform a more perfect lamellar scavenging and to minimize the quantity of so-called blow-by, i.e. the quantity of air-fuel mixture to be discharged without being utilized for the combustion, thus making it possible to realize a reliable and perfect ignition of air-fuel mixture, to improve the fuel consumption, and to minimize the content of poisonous components in the exhaust gas.